Re: What is an interpreter? (Dan Prener)
Sun, 9 May 1993 09:08:41 GMT

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Newsgroups: comp.compilers
From: (Dan Prener)
Keywords: interpreter, design
Organization: IBM T.J. Watson Research Center, Hawthorne, New York
References: 93-05-039
Date: Sun, 9 May 1993 09:08:41 GMT

Paul Robinson <> writes:
> A question I'd like to pose to the readership with respect to either
> program generators or programmable applications. How do we determine when
> something is a "real" interpreter of a "real" language, and when it
> doesn't quite reach that point?

There are two levels at which one could answer this question.

The less interesting of the two is the formal level. One could say that
one of these languages is "real" if it is capable of simulating a
universal Turing machine.

The more interesting level is the practical level. Here I would say that
it is reasonable to accept something less than a universal Turing machine.
Many embedded languages of the sort you refer to have the characteristics
that their designers didn't realize that they were designing a programming
language, and so created a rather poor one. Languages such as "macro"
languages for editors, spreadsheets, debuggers, and the like seem to have
started with the attitude "here is the list of things someone might want
to do, so we'll provide easy ways of doing those." Then some sort of
generality is tacked on just in case. But the history of computing has
shown that users always want to do more than was anticipated by the

I would far prefer a world in which the languages, even "macro" languages,
and the applications were kept orthogonal. Such a world would provide
architected interfaces between the languages and the applications. This
has occasionally been done.
                                                                      Dan Prener (

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